As metastasis (i.e., tumor spread) is the most life-threatening complication of cancer. Identification of genes that regulate the spread of cancer is of utmost importance to reduce cancer deaths. Malignant melanoma serves as a good in vivo model for study of the metastatic process. Understanding the genetic changes in melanoma cells that are responsible for its metastatic phenotype is crucial for improvements in melanoma treatment and survival, and may relate to other solid tumor types as well. The long-term goal of this research is to identify the gene on chromosome 6 (#6) that regulates metastatic potential in cutaneous malignant melanoma. Transfer of a normal copy of #6 into human melanoma cell lines that form tumors and metastasizes in immunodeficient mice results in suppression of tumor spread (i.e. metastasis) without reducing tumor formation. These data suggest that a metastasis-suppressor gene (MSG) is located on #6. More recently, the location of the MSG has been narrowed to 6q16.3-q23 ( about40Mb) by similar studies using #6 fragment. Presently our laboratory has hybrid cells that contain a transferred #6 deleted at 6q21 ( about4Mb), a region frequently lost in many types of advanced cancers. These cells await evaluation in metastasis assays. Thus, the first specific aim is to narrow the region on #6 that encodes the metastasis-suppressor gene by evaluating hybrid melanoma cell lines with a transferred #6 deleted at 6q21 in metastasis assays. The second specific aim will be to further refine the location of the melanoma suppressor gene by identifying BAC, PAC, and/or YAC clones that span the region located at 6q16.3-q23. Selecting overlapping PACs and BACs that cover the region implicated in metastasis suppression will be introduced into the melanoma cell line. Transfected clones will be monitored for suppression of metastasis in immunodeficient mice, These studies will narrow the region of the MSG to <1Mb, which will facilitate its isolation by a combination of cloning techniques. Identification of this gene will shed light on steps in the metastatic process that can be targeted for therapeutic intervention. Gene therapies or novel agents may be designed to restore regulation of cell growth to metastatic cells. Expression of the MSG might be used as a marker to monitor response or to predict patient outcome. In addition, mutational analysis of the gene may provide diagnostic clues that would aid in selection of appropriate treatment regimens that would improve melanoma survival.